Especially brain tumors or vascular deformities are among the diseases which are treated by radiation therapy; even functional targets are radiated. Conventional, invasive, neurosurgical treatment methods are not applicable for all indications, and moreover, they bring with them the disadvantage that a risk of damage to the healthy sections surrounding the focus of the disease frequently arises.
Radiation therapy is an accepted therapeutic method for these diseases, since there is a proven relationship of its action with a therapeutic effect in the patient. E.g., a brain tumor, but also other diseased parts of the body can be treated by means of a linear accelerator. Of course, an exact localization of the diseased sections, of the tumor in this example, is first necessary for this purpose. This localization can be carried out by means of computerized tomography, in which case the patient wears a reference system, usually a head ring in the case of brain tumors, already during the tomography. By precisely localizing and detecting the shape of the tumor, the possibility of reducing the radiation dose on normal tissue presents itself, while, simultaneously, the diseased tissue can be treated with a desired higher dose. With the evaluation of the tomography data, the exact location of the tumor in relation to the reference system is plotted by using three axes of coordinates. The position of the radiation target point, the so-called isocenter, in the tumor is also calculated here. In some cases, it may also be necessary to plot two isocenters.
After the position of the tumor and of the radiation target point is now certain relative to a reference system, which remains on the head or can be arranged again with high accuracy in a reproducible manner, it is necessary to label at least the isocenter for the radiation, so that the isocenter can be hit and treated with the beam of a linear accelerator.
According to the current state of the art, an anchoring means is placed onto the reference system, i.e., the head ring, for this purpose. This anchoring means can have, e.g., the shape of a right parallelepiped consisting of only the lateral edges, which, if it is arranged on the reference system, surrounds the head of the patient. In this case, intermediate mils are, however, arranged between two lateral edges of the right parallelepiped, which are displaceable and adjustable on scales along these lateral edges and thus make it possible for a labeling means, e.g., a prism-shaped body, to be adjusted with the accuracy of the scales on a point of the corresponding surfaces.
A great disadvantage of this device described above concerns the relative inaccuracy with which the projection of the isocenter is adjusted to the respective lateral surfaces of the anchoring means using the scales. This adjustment is made manually and cannot, naturally, exceed the accuracy of the scale (ca. 0.5 mm). However, the exact plotting of the isocenter is very significant particularly for radiation therapy, since damage to the healthy areas surrounding the tumor is to be absolutely avoided.
Another great disadvantage of the prior-art device lies in the fact that the transfer of the data obtained from the tomography to the scale system requires a manual step, in which there is the high risk that the coordinates obtained will be mixed up during the adjustment. In the worst case, such a mix-up can lead to healthy areas of the brain being radiated and thus damaged, in which case, if critical structures are radiated, this can lead to permanent damage in the ability to see or to speak and even to the death of the patient.
Other disadvantages concern the relatively poor clarity of this positioning method, which hardly permits a visual examination of the correctness of the labeling point, and the difficulties in identifying additional data, e.g., the shape of the tumor in the outline. It is also hardly possible to adjust several projections of radiation centers on this device.